The present invention relates to a gas spring, and more particularly, to a gas spring wherein a grease chamber is formed between a seal member and a ring member by mounting the ring member close to the seal member for sealing compressed gas.
Conventionally, a gas spring used in various types of machines generally comprises a cylinder body, a rod member internally slidably fitted in the cylinder body, and a gas chamber which is formed inside the cylinder body and filled with compressed gas (i.e. nitrogen gas). The rod member is forwardly driven by the compressed gas in the gas chamber.
The gas chamber is filled with compressed gas of high pressure (for example, 7 to 10 MPa) for powerful and forward driving of the rod member. In order to maintain the state of high pressure to prevent lowering of the forward driving force, a seal member is mounted between the cylinder body and the rod member, and thus, the compressed gas is sealed and prevented from leaking.
In that case, since the rod member slides against the seal member, friction is generated between the rod member and the seal member. To suppress the wear of the seal member due to friction, grease is usually employed as a lubricant. In the case of a relatively large gas spring, a grease groove is formed by machining the inner periphery of the cylinder body, and the groove is filled with grease. However, in the case of a small-sized gas spring, it is difficult to form such a groove by machining, and therefore grease is coated on the rod member.
In the small-sized gas spring, since grease is applied only to the rod member, the grease is gradually used up as the gas spring is used. As a result, the seal member excessively wears and the surface of the rod member becomes liable to be scratched as well, causing the compressed gas to leak from between the rod member and the seal member, which results in shortening the life of the gas spring.
The object of the present invention is to provide a configuration that enables easy forming of a grease chamber for grease, and to prolong the life of the gas spring.